threadlocal.h

#pragma once
 
/*    Copyright 2014 MongoDB Inc.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
 
#include "mongo/client/undef_macros.h"
#include <boost/thread/tss.hpp>
#include "mongo/client/redef_macros.h"
 
 
namespace mongo { 
 
    /* thread local "value" rather than a pointer
       good for things which have copy constructors (and the copy constructor is fast enough)
       e.g.
         ThreadLocalValue<int> myint;
    */
    template<class T>
    class ThreadLocalValue {
    public:
        ThreadLocalValue( T def = 0 ) : _default( def ) { }
 
        T get() const {
            T * val = _val.get();
            if ( val )
                return *val;
            return _default;
        }
 
        void set( const T& i ) {
            T *v = _val.get();
            if( v ) {
                *v = i;
                return;
            }
            v = new T(i);
            _val.reset( v );
        }
 
        T& getRef() {
            T *v = _val.get();
            if( v ) {
                return *v; 
            }
            v = new T(_default);
            _val.reset( v );
            return *v;
        }
 
    private:
        boost::thread_specific_ptr<T> _val;
        const T _default;
    };
 
    /* TSP
       These macros use intrinsics which are faster than boost::thread_specific_ptr. 
       However the intrinsics don't free up objects on thread closure. Thus we use 
       a combination here, with the assumption that reset's are infrequent, so that 
       get's are fast.
    */
#if defined(MONGO_HAVE___THREAD) || defined(MONGO_HAVE___DECLSPEC_THREAD)
        
    template< class T >
    struct TSP {
        boost::thread_specific_ptr<T> tsp;
    public:
        T* get() const;
        void reset(T* v);
        T* getMake() { 
            T *t = get();
            if( t == 0 )
                reset( t = new T() );
            return t;
        }
    };
 
# if defined(MONGO_HAVE___DECLSPEC_THREAD)
 
#  define TSP_DECLARE(T,p) extern TSP<T> p;
 
#  define TSP_DEFINE(T,p) __declspec( thread ) T* _ ## p; \
    TSP<T> p; \
    template<> T* TSP<T>::get() const { return _ ## p; } \
    void TSP<T>::reset(T* v) { \
        tsp.reset(v); \
        _ ## p = v; \
    } 
# else
 
#  define TSP_DECLARE(T,p) \
    extern __thread T* _ ## p; \
    template<> inline T* TSP<T>::get() const { return _ ## p; } \
    extern TSP<T> p;
 
#  define TSP_DEFINE(T,p) \
    __thread T* _ ## p; \
    template<> void TSP<T>::reset(T* v) { \
        tsp.reset(v); \
        _ ## p = v; \
    } \
    TSP<T> p;
# endif
 
#elif defined(_POSIX_THREADS) && (_POSIX_THREADS >= 0)
    template< class T>
    struct TSP {
        pthread_key_t _key;
    public:
        TSP() {
            verify( pthread_key_create( &_key, TSP::dodelete ) == 0 );
        }
 
        ~TSP() {
            pthread_key_delete( _key );
        }
 
        static void dodelete( void* x ) {
            T* t = reinterpret_cast<T*>(x);
            delete t;
        }
        
        T* get() const { 
            return reinterpret_cast<T*>( pthread_getspecific( _key ) ); 
        }
        
        void reset(T* v) { 
            T* old = get();
            delete old;
            verify( pthread_setspecific( _key, v ) == 0 ); 
        }
 
        T* getMake() { 
            T *t = get();
            if( t == 0 ) {
                t = new T();
                reset( t );
            }
            return t;
        }
    };
 
#  define TSP_DECLARE(T,p) extern TSP<T> p;
 
#  define TSP_DEFINE(T,p) TSP<T> p; 
 
#else
 
    template< class T >
    struct TSP {
        boost::thread_specific_ptr<T> tsp;
    public:
        T* get() const { return tsp.get(); }
        void reset(T* v) { tsp.reset(v); }
        T* getMake() { 
            T *t = get();
            if( t == 0 )
                reset( t = new T() );
            return t;
        }
    };
 
#  define TSP_DECLARE(T,p) extern TSP<T> p;
 
# define TSP_DEFINE(T,p) TSP<T> p; 
 
#endif
 
}